My trials, tribulation and progress in designing and building a handcycle, at home, out of carbon fiber.

Monday, September 16, 2013

Newest Handcycle Design

Newest Handcycle Design... Is it ugly or beauty?

Could you take this home to your mother or would your father have to pull you off to the side and discuss your sanity?

As you can see, during the building process, the design changed a little bit in that I decided to have larger wheel fairing for a better aerodynamic shape. The wheel fairing also take care of a literal problem: getting road debris in my eyes. After one ride on my old handcyle, I had to have an opthamologist remove a splinter embedded in my eye. As well, I lowered the bike another inch or so in comparison to the original design.The bike is very comfortable -- especially the leg holders. I may fall asleep on it on long rides...

One of the better improvements that this handcycle has over the previous version is that there is a center bean that runs from (and including) the neck of the base to nearly the end of the seating area/shoulder area. The beam divides the interior of below-the-seat area. With the strong center beam the bike flexes far less than its predecessor. The center beam is very strong and is composed of a number of layers of biaxial carbon fiber sleeve While this is more expensive as compared to carbon fiber fabric, I am really impressed with the ease of use, integrity and strength. The steering appendage is composed of the same material.The front fork area that takes a lot of stress is composed of about 32 layers of carbon fiber. For further strength in the fork, the leg holders add a lot of structural support. The underside of the leg holders actually curve into the fork (although it is difficult to see from the front). As you can see, there is little frontal area for this design.

During the process of building the last handcycle, I was not at all happy with the front fork's building process. For this one, I decided to build the structural part of the neck-to-fork connection first, insert it into the fork's foam plug, and tie the fork and structure together. This ensured that the neck-to-fork connection would have very close tolerances on fit. This process gave me immeasurably more confidence in the fork.

Handcycle -- Front fork plug and headset

The retractable training wheels are needed. I tried to use my hands-on-the-ground to stabilize the handcycle at a stop, but I just could not balance at the start-up of the bike from a dead stop. After I learn to ride again (that is, balance the handcycle), I hope to add an arduino/motor to raise and lower the stabilizing wheels at, let's say, 6 miles per hour. Of course I am assuming that I ultimately can balance the bike at a higher speed. During my second ride (the ride after adding the retractable stabilizing wheels) I did balance the bike for short periods -- but I also broke a weld joint on retractable wheels assembly. I stupidly used some quick epoxy which was only about 3K PSI in tensile strength. The West Systems epoxy has double the strength. Ultimately I will probably have to reinforce the mechanism for which the retractable wheels rotate back and up.

The chainline is slightly different in the built version as compared to the design. In the end, I decided to have two idlers -- one a power-side idler with a cog (toward the rear of the fork) and one a non-power idler (to the front of the fork). Thus, I have but one chain. The original design called for two chains. From what I read, a single chain with two idlers is more efficient than two chains with an intervening cog set. So far, it appears to be a good decision. I may add a chain guard on the leg holder later but with my bow-leggedness, it is not a problem at this time. Maybe over 100 mile ride I will feel differently.

I continue to use the I-Motion 9 speed transmission (which adds a number of pounds to the bike) but I feel quite certain I could change this to a 9 or 10 speed derailleur if I need different gearing. The nice thing about the I-Motion is its very evenly-spaced gearing. One of the most important features is that II can change gears at a dead stop. Since I cannot stand out of a dead stop, I need to make sure I am in a low gear at fast intersections!

The above chainring is 54 teeth.

The disc brakes are 180mm rotors with the well-known, tried and true, BB7 mechanism.

The front wheel is a 24" while the rear wheel is a 700cc. I built them -- so if they fail, it is indeed my fault!

The bottom bracket is 68mm and is about as low as I can get it while maintaining a very slight clearance for my hands/grips/"pedals" relative to my legs.

The interior foam that formed the plug (to which I added the carbon fiber) is dissolved out with the liberal use of acetone. Matter of fact, I have a bit of the remnants of the foam dotting my driveway.

One aspect of the design improvements on this handcycle is that I can remove the fork from and attach it to the base in a matter of seconds (other than the cables). This can occur because I did a much better job of designing the fork/neck connection structurally and with bearing sets that allow for excellent alignment. The fork's steerer tube is 1" with a permanent top cap of carbon fiber attached to the steerer tube. The top cap allows the steerer tube to be pulled out with ease and for a separation of the fork from the body.

My hydration bags (I usually like to carry 200 oz. of fluids on 100 mile and above rides) will fit into the internal seat area.

The leg holders are very sturdy. There may well be eight or ten layers of carbon fiber in them (I lost track). I fell twice at low speeds (before adding the training wheels) for which the leg holders took the brunt of the impact. I literally could not tell where I hit. My intention was to have the leg holders provide protection -- and they appear to work.

The leg holders provide a stop for excessive turns of the fork. That is, a leg holder will terminate a turn by hitting the base. Over time I may have to shave down the back end of the holders in order to increase the turning angle. Time will tell.

Below is an early view of the handcycle during the building process. Let's call it a comparison of aerodynamic shapes... I like them both! I wish I didn't have to hang all the hardware onto the handcycle though.

2 comments:

Please accept my comments as helpful ideas for you to consider and I am not being critical of your efforts. I love your design and think it is a big step forward from existing designs. Especially as you have successfully solved the starting and stopping issue. The flow of the frame and seat are very aerodynamic. However, I think the front wheel fairing and leg supports are less aero.If you were to reverse the front wheel fairing so the lowest part is at the front, air would flow around and out the fairing rather than get trapped in it. Same for the rear wheel fairing instead of the lowest part in the middle. Likewise with the leg supports. If they were angled low to high - front to rear, or straight with an under the knee rest or footwell on the top they would provide better aerodynamics. Once again you have made a fabulous bicycle and I hope you have many enjoyable rides. Brad

Thanks for the comments. I am building a delta design as a backup to this since I am finding that balancing the bike is difficult (and winter is coming so I need something to fill my evenings and weekends). Please feel free to contact me at bruce.r.chase at gmail... The delta design is interesting in what I hope to achieve on the tail. I am actually using the fork from the first handcycle that I built. Your ideas would be welcomed. From everything I read, about the only way to really get a good design, aerodynamically speaking, is to use a wind-tunnel -- or build a lot of bikes and test them!